The present invention relates to an air-conditioning apparatus for automobiles, and more in particular to an automotive air-conditioning apparatus comprising a variable-capacity compressor.
Conventional air-conditioning apparatuses for automobiles of this type comprise a compressor adapted to operate on several percent of the engine torque as a driving source, and the compressor therefore is required to operate without any loss of efficiency in order to improve the drivability and save fuel for the automobiles. As a result, as disclosed in JP-A-58-85062, such conventional apparatuses comprise a sensor for detecting the physical quantities related to thermal loads including the atmospheric temperature, internal temperature or intake air temperature of an evaporator, and the detection value of the sensor is compared with a set value of the physical quantities related to the thermal loads, so that the capacity of the compressor is controlled in accordance with the magnitude of the error therebetween thereby to regulate the cooling capacity.
The above-mentioned conventional apparatuses also comprise, as disclosed in JP-A-57-175422, means for detecting the engine speed or engine load, and with the increase in engine speed or engine load thus detected, the compressor capacity is reduced to a small level thereby to improve the acceleration characteristic.
Further, the conventional apparatuses mentioned above, as disclosed in JP-A-57-160709, comprise means for detecting the outlet air temperature of an evaporator, and the detection value of the detection means is compared with an actual value of the outlet air temperature of the evaporator, so that a servo motor for controlling the capacity of the compressor is driven in forward or reverse direction depending on the magnitude of the error thus detected, whereby the outlet temperature of the evaporator is regulated to adjust the cooling capacity.
JP-A-59-109527, on the other hand, discloses another conventional apparatus comprising at least means for setting a target of internal temperature and means for detecting the internal temperature, in which the basic control value for driving the compressor is calculated in accordance with the output of the internal temperature target setting means and the internal temperature detection means, and the basic control value is compensated in blowdown mode in accordance with the operation of a mode switch adapted to be changed over to any of a plurality of modes thereby to control the compressor capacity at the time of cooling.
The air-conditioning apparatus for automobiles disclosed in JP-A-58-85062, which is controlled on the basis of physical quantities related to thermal loads such as the atmospheric temperature, internal temperature or intake air temperature of an evaporator, fails to take into consideration the fact that the factor affecting the comfort most strongly is the temperature of blowdown air into the cabin, with the result that the cabin temperature is controlled to a predetermined constant level like in a constant-temperature bath but not to a comfortable blowdown temperature.
In the apparatus disclosed in JP-A-57-175422, on the other hand, with the increase in engine speed or load, the output capacity of a compressor is controlled to a low level arbitrarily without due consideration paid to the required cooling capacity, and therefore the difference between the set temperature and the detection temperature is such that even at the time of cool-down requiring a large cooling capacity, the compressor capacity is reduced to a low level, thereby deteriorating the cooling efficiency for a lower comfort.
The apparatus disclosed in JP-A-57-160709 comprises means for detecting a set value of the output temperature of an evaporator with a detection value, and a servo motor is driven in accordance with the magnitude of the error therebetween, so that response is retarded in refrigeration cycles and no appropriate consideration is given to the time delay caused before a change in the outlet temperature of the evaporator. As a consequence of such a control, the compressor capacity is controlled on the basis of an evaporator outlet temperature not reflecting the control result, thus posing the problem of unstable control of the compressor capacity.
According to the apparatus described in JP-A-59-109527 (UM), the compensation amount of the basic control value is determined only at an average value by a predetermined method of calculations based on the blowdown mode. This compensation method, in which the compensation amount is fixed at a range of average values, fails to effect sufficient compensation to attain a comfortable blowdown temperature, with the result that the loss of the cooling capacity is caused, thereby leading to the problems of energy loss and failure to attain a comfortable blowdown temperature.